1. Field of the Invention
This invention relates to solventless, curable polyorganosiloxane compositions, and in particular, to solventless, curable polyorganosiloxane compositions that can be used to prepare release coatings.
2. Description of the Prior Art
For many years, articles have been made non-adherent to adhesive materials by application of a silicone coating to the articles. Because the composition from which the silicone was coated generally was a highly viscous material, the use of solvents to dilute the silicone composition to a viscosity suitable for coating was required. Increasing pressure from federal, state, and local governments to control or eliminate the emission of solvents into the atmosphere has led manufacturers to develop means for avoiding the use of solvents. Two approaches have received considerable interest: (1) the use of aqueous systems in which the silicone composition is emulsified in water, and (2) solventless systems in which the silicone composition is coatable without the use of solvents.
Although the use of aqueous systems avoids the use of solvents, aqueous systems have not been satisfactory because of the generally poor wetting of many substrates by the aqueous silicone compositions and because of the amount of energy required to remove the water from the coatings.
Solventless silicone compositions generally provide release surfaces that exhibit a sticky or rubbery feel, which is disliked by users of certain types of transfer tapes. Users of large transfer tapes, e.g., tapes consisting of a layer of a pressure-sensitive adhesive borne on a removable silicone release liner, prefer to place the tape on the desired substrate, then press the tape down firmly with their hand or forearm, remove the silicone release liner, and then press the second substrate in contact with the exposed surface of the tape. The users desire that the release liner exhibit a slippery feel so that the friction between the liner and their hand or forearm not bring about chafing of the skin.
Solventless polyorganosiloxane compositions that are useful for providing substrates with a release coating are well known. Compositions comprising a vinylsilyl chain stopped polydiorganosiloxane, a crosslinking polyorganohydrogensiloxane, and a metal hydrosilation catalyst are disclosed in U.S. Pat. Nos. 3,936,581; 4,043,977; 4,162,356; 4,184,006; 4,216,252; 4,256,870; 4,337,332; 4,448,815; 4,609,574; and 4,762,680. None of the compositions disclosed in these patents provide a release surface that would have a slippery feel.
U.S. Pat. No. 4,057,596 discloses a solventless anti-sticking silicone composition comprising (a) a vinyldimethylsilyl end capped polydiorganosiloxane, (b) a hydrogendimethylsilyl end caped polydiorganosiloxane, (c) a polyorganosiloxane having at least three vinylsilyl groups, (d) a polyorganosiloxane having at least three hydrosilyl groups, and (e) a hydrosilation catalyst. The hydrosilation reaction product of such a composition does not have a slippery feel.
Japanese Kokai 61-159480 discloses a solventless composition for providing substrates with a release coating having a slippery feel comprising (1) 100 parts by weight of a polyorganosiloxane having a viscosity of 50 to 10,000 cps and containing 0.5 to 10 mole percent of vinyl group, (2) 0.5 to 30 parts by weight of a polyorganosilicone having a viscosity greater than 100,000 cps and containing fewer vinyl groups than component (1), (3) 0.5 to 50 parts by weight of a polyorganohydrogensiloxane having at least two hydrogen-bonded silicon atoms, and (4) a platinum catalyst. The high viscosity component (2) causes the viscosity of the composition to be greater than is desired and makes the coating of the composition difficult. Compositions of this type do not provide release levels as low as is provided by solvent-based silicone release coating compositions.
Assignee's copending application, U.S. Ser. No. 07/228,282 abandoned Jun. 4, 1990, discloses a silicone-based pressure-sensitive adhesive having high solids content comprising a flowable mixture of (a) a benzene soluble, resinous copolymer having triorganosiloxy and SiO.sub.4/2 units, (b) a diorganoalkenylsiloxy endblocked polydiorganosiloxane, (c) a diorganohydrogensiloxy endblocked polydiorganosiloxane, (d) an organosilicon compound containing more than two groups that will react with a hydrogen or vinyl group of an organopolysiloxane by means of a hydrosilation reaction, and (e) a hydrosilation catalyst in an amount sufficient to effect curing of said composition.
With the exception of Japanese Kokai 61-159480, none of the foregoing disclose solventless release coating compositions that provide coatings having a slippery feel.